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// NamespaceSupport.java - generic Namespace support for SAX.
// http://www.saxproject.org
// Written by David Megginson
// This class is in the Public Domain.  NO WARRANTY!
// $Id: NamespaceSupport.java,v 1.5 2004/11/03 22:53:09 jsuttor Exp $

package org.xml.sax.helpers;

import java.util.EmptyStackException;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;


/**
 * Encapsulate Namespace logic for use by applications using SAX,
 * or internally by SAX drivers.
 *
 * <blockquote>
 * <em>This module, both source code and documentation, is in the
 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
 * for further information.
 * </blockquote>
 *
 * <p>This class encapsulates the logic of Namespace processing: it
 * tracks the declarations currently in force for each context and
 * automatically processes qualified XML names into their Namespace
 * parts; it can also be used in reverse for generating XML qnames
 * from Namespaces.</p>
 *
 * <p>Namespace support objects are reusable, but the reset method
 * must be invoked between each session.</p>
 *
 * <p>Here is a simple session:</p>
 *
 * <pre>
 * String parts[] = new String[3];
 * NamespaceSupport support = new NamespaceSupport();
 *
 * support.pushContext();
 * support.declarePrefix("", "http://www.w3.org/1999/xhtml");
 * support.declarePrefix("dc", "http://www.purl.org/dc#");
 *
 * parts = support.processName("p", parts, false);
 * System.out.println("Namespace URI: " + parts[0]);
 * System.out.println("Local name: " + parts[1]);
 * System.out.println("Raw name: " + parts[2]);
 *
 * parts = support.processName("dc:title", parts, false);
 * System.out.println("Namespace URI: " + parts[0]);
 * System.out.println("Local name: " + parts[1]);
 * System.out.println("Raw name: " + parts[2]);
 *
 * support.popContext();
 * </pre>
 *
 * <p>Note that this class is optimized for the use case where most
 * elements do not contain Namespace declarations: if the same
 * prefix/URI mapping is repeated for each context (for example), this
 * class will be somewhat less efficient.</p>
 *
 * <p>Although SAX drivers (parsers) may choose to use this class to
 * implement namespace handling, they are not required to do so.
 * Applications must track namespace information themselves if they
 * want to use namespace information.
 *
 * @author David Megginson
 * @since SAX 2.0
 */
public class NamespaceSupport {

  ////////////////////////////////////////////////////////////////////
  // Constants.
  ////////////////////////////////////////////////////////////////////


  /**
   * The XML Namespace URI as a constant.
   * The value is <code>http://www.w3.org/XML/1998/namespace</code>
   * as defined in the "Namespaces in XML" * recommendation.
   *
   * <p>This is the Namespace URI that is automatically mapped
   * to the "xml" prefix.</p>
   */
  public final static String XMLNS =
      "http://www.w3.org/XML/1998/namespace";


  /**
   * The namespace declaration URI as a constant.
   * The value is <code>http://www.w3.org/xmlns/2000/</code>, as defined
   * in a backwards-incompatible erratum to the "Namespaces in XML"
   * recommendation.  Because that erratum postdated SAX2, SAX2 defaults
   * to the original recommendation, and does not normally use this URI.
   *
   *
   * <p>This is the Namespace URI that is optionally applied to
   * <em>xmlns</em> and <em>xmlns:*</em> attributes, which are used to
   * declare namespaces.  </p>
   *
   * @see #setNamespaceDeclUris
   * @see #isNamespaceDeclUris
   * @since SAX 2.1alpha
   */
  public final static String NSDECL =
      "http://www.w3.org/xmlns/2000/";


  /**
   * An empty enumeration.
   */
  private final static Enumeration EMPTY_ENUMERATION =
      new Vector().elements();

  ////////////////////////////////////////////////////////////////////
  // Constructor.
  ////////////////////////////////////////////////////////////////////


  /**
   * Create a new Namespace support object.
   */
  public NamespaceSupport() {
    reset();
  }

  ////////////////////////////////////////////////////////////////////
  // Context management.
  ////////////////////////////////////////////////////////////////////


  /**
   * Reset this Namespace support object for reuse.
   *
   * <p>It is necessary to invoke this method before reusing the
   * Namespace support object for a new session.  If namespace
   * declaration URIs are to be supported, that flag must also
   * be set to a non-default value.
   * </p>
   *
   * @see #setNamespaceDeclUris
   */
  public void reset() {
    contexts = new Context[32];
    namespaceDeclUris = false;
    contextPos = 0;
    contexts[contextPos] = currentContext = new Context();
    currentContext.declarePrefix("xml", XMLNS);
  }


  /**
   * Start a new Namespace context.
   * The new context will automatically inherit
   * the declarations of its parent context, but it will also keep
   * track of which declarations were made within this context.
   *
   * <p>Event callback code should start a new context once per element.
   * This means being ready to call this in either of two places.
   * For elements that don't include namespace declarations, the
   * <em>ContentHandler.startElement()</em> callback is the right place.
   * For elements with such a declaration, it'd done in the first
   * <em>ContentHandler.startPrefixMapping()</em> callback.
   * A boolean flag can be used to
   * track whether a context has been started yet.  When either of
   * those methods is called, it checks the flag to see if a new context
   * needs to be started.  If so, it starts the context and sets the
   * flag.  After <em>ContentHandler.startElement()</em>
   * does that, it always clears the flag.
   *
   * <p>Normally, SAX drivers would push a new context at the beginning
   * of each XML element.  Then they perform a first pass over the
   * attributes to process all namespace declarations, making
   * <em>ContentHandler.startPrefixMapping()</em> callbacks.
   * Then a second pass is made, to determine the namespace-qualified
   * names for all attributes and for the element name.
   * Finally all the information for the
   * <em>ContentHandler.startElement()</em> callback is available,
   * so it can then be made.
   *
   * <p>The Namespace support object always starts with a base context
   * already in force: in this context, only the "xml" prefix is
   * declared.</p>
   *
   * @see org.xml.sax.ContentHandler
   * @see #popContext
   */
  public void pushContext() {
    int max = contexts.length;

    contextPos++;

    // Extend the array if necessary
    if (contextPos >= max) {
      Context newContexts[] = new Context[max * 2];
      System.arraycopy(contexts, 0, newContexts, 0, max);
      max *= 2;
      contexts = newContexts;
    }

    // Allocate the context if necessary.
    currentContext = contexts[contextPos];
    if (currentContext == null) {
      contexts[contextPos] = currentContext = new Context();
    }

    // Set the parent, if any.
    if (contextPos > 0) {
      currentContext.setParent(contexts[contextPos - 1]);
    }
  }


  /**
   * Revert to the previous Namespace context.
   *
   * <p>Normally, you should pop the context at the end of each
   * XML element.  After popping the context, all Namespace prefix
   * mappings that were previously in force are restored.</p>
   *
   * <p>You must not attempt to declare additional Namespace
   * prefixes after popping a context, unless you push another
   * context first.</p>
   *
   * @see #pushContext
   */
  public void popContext() {
    contexts[contextPos].clear();
    contextPos--;
    if (contextPos < 0) {
      throw new EmptyStackException();
    }
    currentContext = contexts[contextPos];
  }

  ////////////////////////////////////////////////////////////////////
  // Operations within a context.
  ////////////////////////////////////////////////////////////////////


  /**
   * Declare a Namespace prefix.  All prefixes must be declared
   * before they are referenced.  For example, a SAX driver (parser)
   * would scan an element's attributes
   * in two passes:  first for namespace declarations,
   * then a second pass using {@link #processName processName()} to
   * interpret prefixes against (potentially redefined) prefixes.
   *
   * <p>This method declares a prefix in the current Namespace
   * context; the prefix will remain in force until this context
   * is popped, unless it is shadowed in a descendant context.</p>
   *
   * <p>To declare the default element Namespace, use the empty string as
   * the prefix.</p>
   *
   * <p>Note that there is an asymmetry in this library: {@link
   * #getPrefix getPrefix} will not return the "" prefix,
   * even if you have declared a default element namespace.
   * To check for a default namespace,
   * you have to look it up explicitly using {@link #getURI getURI}.
   * This asymmetry exists to make it easier to look up prefixes
   * for attribute names, where the default prefix is not allowed.</p>
   *
   * @param prefix The prefix to declare, or the empty string to indicate the default element
   * namespace.  This may never have the value "xml" or "xmlns".
   * @param uri The Namespace URI to associate with the prefix.
   * @return true if the prefix was legal, false otherwise
   * @see #processName
   * @see #getURI
   * @see #getPrefix
   */
  public boolean declarePrefix(String prefix, String uri) {
    if (prefix.equals("xml") || prefix.equals("xmlns")) {
      return false;
    } else {
      currentContext.declarePrefix(prefix, uri);
      return true;
    }
  }


  /**
   * Process a raw XML qualified name, after all declarations in the
   * current context have been handled by {@link #declarePrefix
   * declarePrefix()}.
   *
   * <p>This method processes a raw XML qualified name in the
   * current context by removing the prefix and looking it up among
   * the prefixes currently declared.  The return value will be the
   * array supplied by the caller, filled in as follows:</p>
   *
   * <dl>
   * <dt>parts[0]</dt>
   * <dd>The Namespace URI, or an empty string if none is
   * in use.</dd>
   * <dt>parts[1]</dt>
   * <dd>The local name (without prefix).</dd>
   * <dt>parts[2]</dt>
   * <dd>The original raw name.</dd>
   * </dl>
   *
   * <p>All of the strings in the array will be internalized.  If
   * the raw name has a prefix that has not been declared, then
   * the return value will be null.</p>
   *
   * <p>Note that attribute names are processed differently than
   * element names: an unprefixed element name will receive the
   * default Namespace (if any), while an unprefixed attribute name
   * will not.</p>
   *
   * @param qName The XML qualified name to be processed.
   * @param parts An array supplied by the caller, capable of holding at least three members.
   * @param isAttribute A flag indicating whether this is an attribute name (true) or an element
   * name (false).
   * @return The supplied array holding three internalized strings representing the Namespace URI
   * (or empty string), the local name, and the XML qualified name; or null if there is an
   * undeclared prefix.
   * @see #declarePrefix
   * @see java.lang.String#intern
   */
  public String[] processName(String qName, String parts[],
      boolean isAttribute) {
    String myParts[] = currentContext.processName(qName, isAttribute);
    if (myParts == null) {
      return null;
    } else {
      parts[0] = myParts[0];
      parts[1] = myParts[1];
      parts[2] = myParts[2];
      return parts;
    }
  }


  /**
   * Look up a prefix and get the currently-mapped Namespace URI.
   *
   * <p>This method looks up the prefix in the current context.
   * Use the empty string ("") for the default Namespace.</p>
   *
   * @param prefix The prefix to look up.
   * @return The associated Namespace URI, or null if the prefix is undeclared in this context.
   * @see #getPrefix
   * @see #getPrefixes
   */
  public String getURI(String prefix) {
    return currentContext.getURI(prefix);
  }


  /**
   * Return an enumeration of all prefixes whose declarations are
   * active in the current context.
   * This includes declarations from parent contexts that have
   * not been overridden.
   *
   * <p><strong>Note:</strong> if there is a default prefix, it will not be
   * returned in this enumeration; check for the default prefix
   * using the {@link #getURI getURI} with an argument of "".</p>
   *
   * @return An enumeration of prefixes (never empty).
   * @see #getDeclaredPrefixes
   * @see #getURI
   */
  public Enumeration getPrefixes() {
    return currentContext.getPrefixes();
  }


  /**
   * Return one of the prefixes mapped to a Namespace URI.
   *
   * <p>If more than one prefix is currently mapped to the same
   * URI, this method will make an arbitrary selection; if you
   * want all of the prefixes, use the {@link #getPrefixes}
   * method instead.</p>
   *
   * <p><strong>Note:</strong> this will never return the empty (default) prefix;
   * to check for a default prefix, use the {@link #getURI getURI}
   * method with an argument of "".</p>
   *
   * @param uri the namespace URI
   * @return one of the prefixes currently mapped to the URI supplied, or null if none is mapped or
   * if the URI is assigned to the default namespace
   * @see #getPrefixes(java.lang.String)
   * @see #getURI
   */
  public String getPrefix(String uri) {
    return currentContext.getPrefix(uri);
  }


  /**
   * Return an enumeration of all prefixes for a given URI whose
   * declarations are active in the current context.
   * This includes declarations from parent contexts that have
   * not been overridden.
   *
   * <p>This method returns prefixes mapped to a specific Namespace
   * URI.  The xml: prefix will be included.  If you want only one
   * prefix that's mapped to the Namespace URI, and you don't care
   * which one you get, use the {@link #getPrefix getPrefix}
   * method instead.</p>
   *
   * <p><strong>Note:</strong> the empty (default) prefix is <em>never</em> included
   * in this enumeration; to check for the presence of a default
   * Namespace, use the {@link #getURI getURI} method with an
   * argument of "".</p>
   *
   * @param uri The Namespace URI.
   * @return An enumeration of prefixes (never empty).
   * @see #getPrefix
   * @see #getDeclaredPrefixes
   * @see #getURI
   */
  public Enumeration getPrefixes(String uri) {
    Vector prefixes = new Vector();
    Enumeration allPrefixes = getPrefixes();
    while (allPrefixes.hasMoreElements()) {
      String prefix = (String) allPrefixes.nextElement();
      if (uri.equals(getURI(prefix))) {
        prefixes.addElement(prefix);
      }
    }
    return prefixes.elements();
  }


  /**
   * Return an enumeration of all prefixes declared in this context.
   *
   * <p>The empty (default) prefix will be included in this
   * enumeration; note that this behaviour differs from that of
   * {@link #getPrefix} and {@link #getPrefixes}.</p>
   *
   * @return An enumeration of all prefixes declared in this context.
   * @see #getPrefixes
   * @see #getURI
   */
  public Enumeration getDeclaredPrefixes() {
    return currentContext.getDeclaredPrefixes();
  }

  /**
   * Controls whether namespace declaration attributes are placed
   * into the {@link #NSDECL NSDECL} namespace
   * by {@link #processName processName()}.  This may only be
   * changed before any contexts have been pushed.
   *
   * @throws IllegalStateException when attempting to set this after any context has been pushed.
   * @since SAX 2.1alpha
   */
  public void setNamespaceDeclUris(boolean value) {
    if (contextPos != 0) {
      throw new IllegalStateException();
    }
    if (value == namespaceDeclUris) {
      return;
    }
    namespaceDeclUris = value;
    if (value) {
      currentContext.declarePrefix("xmlns", NSDECL);
    } else {
      contexts[contextPos] = currentContext = new Context();
      currentContext.declarePrefix("xml", XMLNS);
    }
  }

  /**
   * Returns true if namespace declaration attributes are placed into
   * a namespace.  This behavior is not the default.
   *
   * @since SAX 2.1alpha
   */
  public boolean isNamespaceDeclUris() {
    return namespaceDeclUris;
  }

  ////////////////////////////////////////////////////////////////////
  // Internal state.
  ////////////////////////////////////////////////////////////////////

  private Context contexts[];
  private Context currentContext;
  private int contextPos;
  private boolean namespaceDeclUris;

  ////////////////////////////////////////////////////////////////////
  // Internal classes.
  ////////////////////////////////////////////////////////////////////

  /**
   * Internal class for a single Namespace context.
   *
   * <p>This module caches and reuses Namespace contexts,
   * so the number allocated
   * will be equal to the element depth of the document, not to the total
   * number of elements (i.e. 5-10 rather than tens of thousands).
   * Also, data structures used to represent contexts are shared when
   * possible (child contexts without declarations) to further reduce
   * the amount of memory that's consumed.
   * </p>
   */
  final class Context {

    /**
     * Create the root-level Namespace context.
     */
    Context() {
      copyTables();
    }


    /**
     * (Re)set the parent of this Namespace context.
     * The context must either have been freshly constructed,
     * or must have been cleared.
     *
     * @param context The parent Namespace context object.
     */
    void setParent(Context parent) {
      this.parent = parent;
      declarations = null;
      prefixTable = parent.prefixTable;
      uriTable = parent.uriTable;
      elementNameTable = parent.elementNameTable;
      attributeNameTable = parent.attributeNameTable;
      defaultNS = parent.defaultNS;
      declSeen = false;
    }

    /**
     * Makes associated state become collectible,
     * invalidating this context.
     * {@link #setParent} must be called before
     * this context may be used again.
     */
    void clear() {
      parent = null;
      prefixTable = null;
      uriTable = null;
      elementNameTable = null;
      attributeNameTable = null;
      defaultNS = null;
    }


    /**
     * Declare a Namespace prefix for this context.
     *
     * @param prefix The prefix to declare.
     * @param uri The associated Namespace URI.
     * @see org.xml.sax.helpers.NamespaceSupport#declarePrefix
     */
    void declarePrefix(String prefix, String uri) {
      // Lazy processing...
//          if (!declsOK)
//              throw new IllegalStateException (
//                  "can't declare any more prefixes in this context");
      if (!declSeen) {
        copyTables();
      }
      if (declarations == null) {
        declarations = new Vector();
      }

      prefix = prefix.intern();
      uri = uri.intern();
      if ("".equals(prefix)) {
        if ("".equals(uri)) {
          defaultNS = null;
        } else {
          defaultNS = uri;
        }
      } else {
        prefixTable.put(prefix, uri);
        uriTable.put(uri, prefix); // may wipe out another prefix
      }
      declarations.addElement(prefix);
    }


    /**
     * Process an XML qualified name in this context.
     *
     * @param qName The XML qualified name.
     * @param isAttribute true if this is an attribute name.
     * @return An array of three strings containing the URI part (or empty string), the local part,
     * and the raw name, all internalized, or null if there is an undeclared prefix.
     * @see org.xml.sax.helpers.NamespaceSupport#processName
     */
    String[] processName(String qName, boolean isAttribute) {
      String name[];
      Hashtable table;

      // Select the appropriate table.
      if (isAttribute) {
        table = attributeNameTable;
      } else {
        table = elementNameTable;
      }

      // Start by looking in the cache, and
      // return immediately if the name
      // is already known in this content
      name = (String[]) table.get(qName);
      if (name != null) {
        return name;
      }

      // We haven't seen this name in this
      // context before.  Maybe in the parent
      // context, but we can't assume prefix
      // bindings are the same.
      name = new String[3];
      name[2] = qName.intern();
      int index = qName.indexOf(':');

      // No prefix.
      if (index == -1) {
        if (isAttribute) {
          if (qName == "xmlns" && namespaceDeclUris) {
            name[0] = NSDECL;
          } else {
            name[0] = "";
          }
        } else if (defaultNS == null) {
          name[0] = "";
        } else {
          name[0] = defaultNS;
        }
        name[1] = name[2];
      }

      // Prefix
      else {
        String prefix = qName.substring(0, index);
        String local = qName.substring(index + 1);
        String uri;
        if ("".equals(prefix)) {
          uri = defaultNS;
        } else {
          uri = (String) prefixTable.get(prefix);
        }
        if (uri == null
            || (!isAttribute && "xmlns".equals(prefix))) {
          return null;
        }
        name[0] = uri;
        name[1] = local.intern();
      }

      // Save in the cache for future use.
      // (Could be shared with parent context...)
      table.put(name[2], name);
      return name;
    }


    /**
     * Look up the URI associated with a prefix in this context.
     *
     * @param prefix The prefix to look up.
     * @return The associated Namespace URI, or null if none is declared.
     * @see org.xml.sax.helpers.NamespaceSupport#getURI
     */
    String getURI(String prefix) {
      if ("".equals(prefix)) {
        return defaultNS;
      } else if (prefixTable == null) {
        return null;
      } else {
        return (String) prefixTable.get(prefix);
      }
    }


    /**
     * Look up one of the prefixes associated with a URI in this context.
     *
     * <p>Since many prefixes may be mapped to the same URI,
     * the return value may be unreliable.</p>
     *
     * @param uri The URI to look up.
     * @return The associated prefix, or null if none is declared.
     * @see org.xml.sax.helpers.NamespaceSupport#getPrefix
     */
    String getPrefix(String uri) {
      if (uriTable == null) {
        return null;
      } else {
        return (String) uriTable.get(uri);
      }
    }


    /**
     * Return an enumeration of prefixes declared in this context.
     *
     * @return An enumeration of prefixes (possibly empty).
     * @see org.xml.sax.helpers.NamespaceSupport#getDeclaredPrefixes
     */
    Enumeration getDeclaredPrefixes() {
      if (declarations == null) {
        return EMPTY_ENUMERATION;
      } else {
        return declarations.elements();
      }
    }


    /**
     * Return an enumeration of all prefixes currently in force.
     *
     * <p>The default prefix, if in force, is <em>not</em>
     * returned, and will have to be checked for separately.</p>
     *
     * @return An enumeration of prefixes (never empty).
     * @see org.xml.sax.helpers.NamespaceSupport#getPrefixes
     */
    Enumeration getPrefixes() {
      if (prefixTable == null) {
        return EMPTY_ENUMERATION;
      } else {
        return prefixTable.keys();
      }
    }

    ////////////////////////////////////////////////////////////////
    // Internal methods.
    ////////////////////////////////////////////////////////////////


    /**
     * Copy on write for the internal tables in this context.
     *
     * <p>This class is optimized for the normal case where most
     * elements do not contain Namespace declarations.</p>
     */
    private void copyTables() {
      if (prefixTable != null) {
        prefixTable = (Hashtable) prefixTable.clone();
      } else {
        prefixTable = new Hashtable();
      }
      if (uriTable != null) {
        uriTable = (Hashtable) uriTable.clone();
      } else {
        uriTable = new Hashtable();
      }
      elementNameTable = new Hashtable();
      attributeNameTable = new Hashtable();
      declSeen = true;
    }

    ////////////////////////////////////////////////////////////////
    // Protected state.
    ////////////////////////////////////////////////////////////////

    Hashtable prefixTable;
    Hashtable uriTable;
    Hashtable elementNameTable;
    Hashtable attributeNameTable;
    String defaultNS = null;

    ////////////////////////////////////////////////////////////////
    // Internal state.
    ////////////////////////////////////////////////////////////////

    private Vector declarations = null;
    private boolean declSeen = false;
    private Context parent = null;
  }
}

// end of NamespaceSupport.java
